Method of bonding nonwoven textile webs



June 24, 1969 c; 0, N 3,452,128

METHOD OF BONDING NONWOVEN TEXTILE WEBS Filed May 15, 1967 INVENTOR.C.O. RAI NS A T TORNEVS United States Patent US. Cl. 264126 9 ClaimsABSTRACT OF THE DISCLOSURE A method of preparing a mat of fiberscontaining at least some thermoplastic fibers arranged in either orderedor random orientation which are bonded into a coherent web by at leastpartial fusing while the web is passed vertically through the nip of twoheated rollers.

BACKGROUND OF THE INVENTION It is known in the art that nonwovencoherent webs can be formed by depositing a mass of fibers in eitherrandom or ordered orientation to form a mat, and bonding the fiberstogether to form a web. One method of bonding the fibers is to pass themat through a heating device wherein at least a portion of the fibers inthe mat fuse, interlocking the individual fibers into a coherent web.This heating has been accomplished in a number of ways, none of whichhas proved entirely satisfactory for certain types of fabrics. A majordifiiculty with the prior art methods lies in the fact that the heatingstep must be carefully controlled to insure that the fibers are broughtto the correct temperature and maintained at that temperature for theproper length of time and under carefully controlled pressure in orderto produce the desired end product. Overheating of the mat will resultin total fusion of the fibers, which is often undesirable, whileunderheating will cause insufiicient fusion, resulting in a structurallyweak web.

It is therefore an object of this invention to provide a method forbonding fibers into a coherent web under carefully controlled conditionsof temperature and pressure whereby a web of uniform quality can beobtained.

SUMMARY OF THE INVENTION According to my invention, the thermoplasticfibers in a mat are fused together by passing that mat verticallythrough the nip between two heated rollers. The passage of that mat in avertical direction, either upwardly or downwardly, is necessary toobtain consistent quality in the bonded web. Attempts to practice myinvention by passing the mat of fibers horizontally through a nip havebeen largely unsuccessful, apparently because of the tendency of the matto wrap around the heated rollers with the consequent inability toclosely control the length of time of the heating step.

DESCRIPTION OF THE DRAWING The operation of my invention can be seen byreference to the drawing. A mat of fibers, which may or may not beinterentangled, is shown at 1. This mat passes over retractable feedroll 2, and then passes vertically through the nip between heatedrollers 3 and 4. These heated rollers are conveniently heated by steamor electrical coils, and are maintained at a temperature suitable tocause fusion of fibers within the mat. The pressure exerted on thefibers is determined by the size of the nip gap. This gap is ordinarilyfrom 0.010 to 0.020 inch, depending upon the thickness of the mat andthe desired pressure. The bonded web is passed over discharge roller 5to further processing or packaging operations.

3,452,128 Patented June 24, 1969 In order to prevent overheating in caseof stoppage of the mat travel, heated roller 4 is retractable by meansof hydraulic cylinder 7 to the position indicated by dotted lines 6. Thegap between the two heated rollers when roller 4 is retracted isconveniently about 6 inches. The actuating device (not shown) whichoperates hydraulic cylinder 7 is also operatively attached to hydrauliccylinder 8. This cylinder advances the feed roller 2 horizontally abouthalf the distance of the retraction of heated roller 4. Thus, the twohydraulic cylinders acting at the same time will open a gap between thetwo heated rollers, and simultaneously move the web formed to becentered between the two rollers, and out of contact with both of them.The actuating mechanism which operates hydraulic cylinders 7 and 8 isone which senses any stoppage of travel of the mat, and could beconveniently located on feed roll 2, discharge roll 5, or at any otherpoint of the fiber feeding or web takeup means.

DESCRIPTION OF THE PREFERRED EMBODIMENT The process of my invention canbe used with any mat containing fusible organic thermoplastic fibers.The mat can consist entirely of such fusible fibers, or it can be ablend of fusible fibers with other synthetic or natural fibrousmaterials.

The mat may be formed by any conventional means. For example, the fiberscould be supplied from a carding machine in the form of aunidirectionally oriented web, in which case all fibers would beoriented in the direction of the mat travel. Alternately, the fiberscould be crosslapped by layering a unidirectionally oriented web fromone or more cards or garnetts back and forth on a moving conveyor. Inanother embodiment, the fibers could be deposited on a conveyor belt byair deposition, giving a random orientation.

Mats formed by any of the above methods can be taken directly to thebonding process of my invention, or can be subjected to some preliminarytreatment which would increase the coherency of the mat prior to heatbonding. In a preferred embodiment, the mat is subjected to aconventional textile needling operation prior to the fusion bondingprocess. When the mat is so needled, it can be observed that there is adifference in the two surfaces of them at. The side on which the needlesenter is smoother than the other or nap side, and, in order to obtainsatisfactory fusion, it is necessary to use a slightly higher rolltemperature on the smooth side than on the nap side of the mat. Thetemperature difference between the two rolls in this embodiment isgenerally in the order of 5 to 10 F.

The heat fusible materials which can be used in forming mats for theprocess of my invention include substantially all of the syntheticorganic thermoplastic materials. Polyolefins, such as the polymers ofethylene, propylene, butene, and copolymers thereof, are partic ularlysuitable. Also suitable are polyesters, polyamides, palyurethanes,cellulosics, and other known organic thermoplastics which are capable ofbeing formed into filaments.

The characteristics of the bonded webs produced by the process of myinvention can vary widely. By using high temperatures and small nip gapclearance, I can produce completely fused paper-like webs. By using onlya small proportion of fibers which are fusible at the roll temperature,and providing a large nip gap, I can produce a very low densitybatting-like web. Intermediate density webs are produced by variationsin temperature and nip gap clearance.

By use of blends of materials I can also vary the properties of the webproduced. For example, a blend of about 20-25 percent fusiblepolyethylene with wool fibers 3 forms a good insulating batting. A blendof a small proportion of fusible polyethylene with foamed and crimpedfilaments of high melting point polyolefin, polyurethane or othersynthetic filaments forms a batting-like web of excellent insulatingproperties, and one which is non-allergenic and resistant to organismgrowth.

Webs of fibers which are partly or completely fused have many textileapplications; polypropylene web of medium density is suitable, forexample, for carpet backing.

The temperature of said rollers will vary depending upon the meltingpoint of the fusible fibers used. Generally the temperature of therollers will be from about 300 F. to about 400 F.

The clearance in the nip will vary depending upon the thickness of themat and the desired degree of compression and fusing. In general, a nipgap of .010" to .020" is suitable, but gaps considerably larger can beused for thick batting.

Reasonable variation and modification are permissible Within the scopeof my invention without departing from the spirit thereof.

1 claim:

1. In a process for forming a non-woven a bonded web comprisingsynthetic organic thermoplastic fibers, wherein said fibers areaccumulated in the form of a mat and said mat is exposed to sufiicientheat and pressure to fuse at least some ofsaid thermoplastic fibers andbond said fibers into a coherent web, the improvement comprisingapplying said heat and pressure by pass- 30 ing said mat verticallythrough the nip of a pair of heated rollers.

2. The process of claim 1, wherein the web, prior to the heating andpressing, comprises a mat of interentangled fibers.

3. The process of claim 1, where the web, prior to the heating andpressing, comprises a conventionally needled mat having a smooth sideand a nap side.

4. The process of claim 3, wherein the roller adjacent said smooth sideof said needled mat is at a higher temperature than the roller adjacentsaid nap side of the mat.

5. The process of claim 1 wherein said fibers are selected frompolyolefins, polyesters, polyamides, polyurethanes, and cellulosics, andblends thereof.

6. The process of claim 1 wherein only a portion of the fibers in saidmat are fusible at the temperature and pressure conditions in the nip ofsaid rollers.

7. The process of claim 1, wherein the web, prior to the heating andpressing, comprises unidirectionally oriented fibers.

8. The process of claim 1, wherein the Web, prior to the heating andpressing, comprises crosslaid fibers.

9. The process of claim 1, wherein the web, prior to the heating andpressing comprises randomly oriented fibers.

References Cited UNITED STATES PATENTS 2,688,380 9/1954 MacHenry 156-180FOREIGN PATENTS 642,522 6/ 1962 Canada.

DONALD J. ARNOLD, Primary Examiner.

J. R. HALL, Assistant Examiner.

US. Cl. X.R.

